1. Field of the Invention
This invention relates to an alkaline battery, such as nickel-cadmium, nickel-zinc, silver-zinc, etc. and more particularly to an alkaline battery which has a high discharge rate performance, a savings of materials and is easy to manufacture.
2. Description of the Prior Art
Taking a nickel-cadmium battery as an example of alkaline batteries, the battery consists essentially of a pair of electrodes, one a positive plate and the other a negative plate, a separator and a container.
Preparation of the positive or negative plates requires the sintering of a fine nickel powder on a metal carrier such as a punched metal or a woven wire screen. The positive electrode is made by impregnating hydrated nickel on the sintered plate as an active material and the negative electrode is made by impregnating hydrated cadmium on the sintered plate.
The battery cell is assembled by rolling both electrodes, separated by an insulation layer into a tight roll or core or by stacking them alternately.
As a method for affixing current collectors to each electrode, it is well known to form a current collector on the metal carrier by punching prior to the sintering process or to affix the current collector by welding a collecting terminal to the electrode after the impregnation of active materials.
However, in the former, material loss is inevitable due to the remaining parts of said metal carrier which are cut or punched. Furthermore, a complex process for cutting or punching of the current collector is required.
Also, the concentration of the current collecting point on said electrode has the disadvantage of causing low discharge rates for the cell. In the latter method, the process of welding the current collector on the electrode after impregnation with active materials is an extremely difficult technique and has the same disadvantage of low discharge rates for the cell.
U.S. Pat. No. 3,732,124 discloses an improved method for affixing the current collector to overcome the disadvantages explained above. In the method of this patent, a cell has an assembly of electrodes and separators. Opposite sides or ends of the electrodes have bared parts of the metal carriers, the projecting bared parts being respectively welded at the ends or sides of the assembly to a current collector member. The cell is further characterized in that each current collector member comprises edges substantially perpendicular to its principal plane and the edges being embedded by welding into the bared projecting parts of the respective electrodes. Consequently, the cell is more rugged and can bear higher discharge rates than the cell employing the previously described collectors.
As a result of practical application, it has been observed that the process described in U.S. Pat. No. 3,732,124 has several disadvantages which make it impractical. Namely, since the current collector and electrode are welded only at the embedded bent portion of the collector, joint strength between them is not enough and not reliable from a mass production stand point. Furthermore, in order to insure the embedding of the current collector into the electrode, sufficient size of the bared projection portion at the edge of each electrode is required.